1. Technical Field
An embodiment of the invention generally relates to mounting optical and electrical devices to a substrate while coupling to an optical waveguide integrated on a printed circuit board. More particularly, the present invention relates to using conventional flip-chip packaging to integrate optical and electrical devices to a printed circuit board while simultaneously coupling the optical devices to an optical waveguide by utilizing an integrated microlens array.
2. Discussion of the Related Art
Electrical systems often use a number of integrated circuits that are mounted on a printed circuit board. Each integrated circuit includes a number of leads that extend from the packaging of the circuit. The leads of the various integrated circuits are interconnected to allow signals to be passed between the integrated circuits such that the system performs some function. For example, a personal computer includes a wide variety of integrated circuits, e.g., a microprocessor and memory chips, that are interconnected on one or more printed circuit boards in the computer.
Printed circuit boards are used to bring together separately fabricated integrated circuits. However, the use of printed circuit boards creates some problems that are not so easily overcome. A printed circuit board includes metal traces to transmit an electrical signal between the various integrated circuits. As the number of components on a printed circuit board increases, the number of metal traces needed to connect the components also increases. This fact decreases the spacing between the metal traces, which can lead to capacitance problems between the metal traces and space constraints due to the limited area available on the printed circuit board for metal traces. It is desirable to reduce the amount of physical space required by such printed circuit boards. Also, it is desirable to reduce the physical length of electrical interconnections between devices because of concerns with signal loss or dissipation and interference with and by other integrated circuitry devices.
As the density of electronic integrated circuits increases, the limiting factor for circuit speed increasingly becomes propagation delay due to capacitance associated with circuit interconnection. At relatively low clock speeds, the capacitive loading is not a significant factor. As newer applications push clock speeds into the one hundred megahertz range and beyond, capacitive loading becomes a limiting factor for circuit performance by limiting circuit speed and increasing circuit cross talk.
A continuing challenge in the semiconductor industry is to find new, innovative, and efficient ways of forming electrical connections with and between circuit devices that are fabricated on the same, and on different, wafers or dies. Relatedly, continuing challenges are posed to find and/or improve upon the packaging techniques utilized to package integrated circuitry devices. As device dimensions continue to shrink, these challenges become even more important.
One approach utilizes optical interconnection to transmit optical signals between components, particularly components located on remote regions of a board. The optical signals are composed of modulated light beams that carry data between components. An optical emitter, such as a laser, is mounted on one region of the board and emits the optical signal. The optical signals are diffracted by holographic elements into a optical waveguide. The optical signals then propagate from one point to another through the optical waveguide before being diffracted out of the optical waveguide by holographic elements and focused upon opto-electronic receivers on the surface of an integrated circuit.
However, the interface between the component, i.e., the emitter or detector, and the optical waveguide is difficult to fabricate. In this approach, holographic routing elements have to be precisely aligned with the opto-electronic receivers of the integrated circuits. The opto-electronic transmitters then have to be precisely aligned relative to the holographic routing elements in order for the modulated light beams emitted by the sources to be directed by the holographic routing element to the proper opto-electronic receivers. Achieving the required precision of alignment makes assembly into a package extremely challenging. The kinds of tolerances required are normally associated with semiconductor device fabrication processes rather than with package assembly.
Another limitation of the prior art is the lack of flexibility in the assembly of printed circuit boards. Because the optical emitters, holographic elements, waveguides, and optical detectors must be mounted during assembly of the printed circuit board, there is no flexibility in adding any of these elements or adjusting their position once the printed circuit board has been fabricated.
For reasons stated above, and for other reasons which will become apparent to those in the art upon reading and understanding the present specification, there is a need in the art for an improved technique for interconnecting individual integrated circuits in an electronic system.